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    SubjectRe: [PATCH 03/10] ftrace: fix sched_switch API
    2008/11/8 Steven Rostedt <rostedt@goodmis.org>:
    > Impact: fix for sched_switch that broke dynamic ftrace startup
    >
    > The commit: tracing/fastboot: use sched switch tracer from boot tracer
    > broke the API of the sched_switch trace. The use of the
    > tracing_start/stop_cmdline record is for only recording the cmdline,
    > NOT recording the schedule switches themselves.
    >
    > Seeing that the boot tracer broke the API to do something that it
    > wanted, this patch adds a new interface for the API while
    > puting back the original interface of the old API.
    >
    > Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    > CC: Frederic Weisbecker <fweisbec@gmail.com>
    > ---
    > kernel/trace/trace.h | 4 ++-
    > kernel/trace/trace_boot.c | 6 ++--
    > kernel/trace/trace_sched_switch.c | 50 +++++++++++++++++++++++++++++-------
    > 3 files changed, 46 insertions(+), 14 deletions(-)
    >
    > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
    > index db12e16..25abfc4 100644
    > --- a/kernel/trace/trace.h
    > +++ b/kernel/trace/trace.h
    > @@ -324,7 +324,9 @@ void trace_function(struct trace_array *tr,
    >
    > void tracing_start_cmdline_record(void);
    > void tracing_stop_cmdline_record(void);
    > -void tracing_cmdline_assign_trace(struct trace_array *tr);
    > +void tracing_sched_switch_assign_trace(struct trace_array *tr);
    > +void tracing_stop_sched_switch_record(void);
    > +void tracing_start_sched_switch_record(void);
    > int register_tracer(struct tracer *type);
    > void unregister_tracer(struct tracer *type);
    >
    > diff --git a/kernel/trace/trace_boot.c b/kernel/trace/trace_boot.c
    > index 662cb91..0203c10 100644
    > --- a/kernel/trace/trace_boot.c
    > +++ b/kernel/trace/trace_boot.c
    > @@ -28,13 +28,13 @@ void start_boot_trace(void)
    > void enable_boot_trace(void)
    > {
    > if (pre_initcalls_finished)
    > - tracing_start_cmdline_record();
    > + tracing_start_sched_switch_record();
    > }
    >
    > void disable_boot_trace(void)
    > {
    > if (pre_initcalls_finished)
    > - tracing_stop_cmdline_record();
    > + tracing_stop_sched_switch_record();
    > }
    >
    > static void reset_boot_trace(struct trace_array *tr)
    > @@ -55,7 +55,7 @@ static void boot_trace_init(struct trace_array *tr)
    > for_each_cpu_mask(cpu, cpu_possible_map)
    > tracing_reset(tr, cpu);
    >
    > - tracing_cmdline_assign_trace(tr);
    > + tracing_sched_switch_assign_trace(tr);
    > }
    >
    > static void boot_trace_ctrl_update(struct trace_array *tr)
    > diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
    > index fbf05df..79410db 100644
    > --- a/kernel/trace/trace_sched_switch.c
    > +++ b/kernel/trace/trace_sched_switch.c
    > @@ -125,20 +125,16 @@ static void tracing_sched_unregister(void)
    > static void tracing_start_sched_switch(void)
    > {
    > mutex_lock(&sched_register_mutex);
    > - if (!(sched_ref++)) {
    > - tracer_enabled = 1;
    > + if (!(sched_ref++))
    > tracing_sched_register();
    > - }
    > mutex_unlock(&sched_register_mutex);
    > }
    >
    > static void tracing_stop_sched_switch(void)
    > {
    > mutex_lock(&sched_register_mutex);
    > - if (!(--sched_ref)) {
    > + if (!(--sched_ref))
    > tracing_sched_unregister();
    > - tracer_enabled = 0;
    > - }
    > mutex_unlock(&sched_register_mutex);
    > }
    >
    > @@ -153,14 +149,48 @@ void tracing_stop_cmdline_record(void)
    > }
    >
    > /**
    > - * tracing_cmdline_assign_trace - assign a trace array for ctx switch
    > + * tracing_start_sched_switch_record - start tracing context switches
    > + *
    > + * Turns on context switch tracing for a tracer.
    > + */
    > +void tracing_start_sched_switch_record(void)
    > +{
    > + if (unlikely(!ctx_trace)) {
    > + WARN_ON(1);
    > + return;
    > + }
    > +
    > + tracing_start_sched_switch();
    > +
    > + mutex_lock(&sched_register_mutex);
    > + tracer_enabled++;
    > + mutex_unlock(&sched_register_mutex);
    > +}
    > +
    > +/**
    > + * tracing_stop_sched_switch_record - start tracing context switches
    > + *
    > + * Turns off context switch tracing for a tracer.
    > + */
    > +void tracing_stop_sched_switch_record(void)
    > +{
    > + mutex_lock(&sched_register_mutex);
    > + tracer_enabled--;
    > + WARN_ON(tracer_enabled < 0);
    > + mutex_unlock(&sched_register_mutex);
    > +
    > + tracing_stop_sched_switch();
    > +}
    > +
    > +/**
    > + * tracing_sched_switch_assign_trace - assign a trace array for ctx switch
    > * @tr: trace array pointer to assign
    > *
    > * Some tracers might want to record the context switches in their
    > * trace. This function lets those tracers assign the trace array
    > * to use.
    > */
    > -void tracing_cmdline_assign_trace(struct trace_array *tr)
    > +void tracing_sched_switch_assign_trace(struct trace_array *tr)
    > {
    > ctx_trace = tr;
    > }
    > @@ -168,12 +198,12 @@ void tracing_cmdline_assign_trace(struct trace_array *tr)
    > static void start_sched_trace(struct trace_array *tr)
    > {
    > sched_switch_reset(tr);
    > - tracing_start_cmdline_record();
    > + tracing_start_sched_switch_record();
    > }
    >
    > static void stop_sched_trace(struct trace_array *tr)
    > {
    > - tracing_stop_cmdline_record();
    > + tracing_stop_sched_switch_record();
    > }
    >
    > static void sched_switch_trace_init(struct trace_array *tr)


    Sorry, I misunderstood the sense of these functions and then used them only for
    what they did: start/stop sched event capture.

    Acked-by: Frederic Weisbecker < fweisbec@gmail.com>


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